In common with all animals, oogenesis in Xenopus laevis, the South African clawed frog, is characterized by a massive accumulation of mitochondria that appear to provide the sole source of mitochondria for the developing embryo. Mitochondrial biogenesis in this system has been shown to be completed by the time the oocyte is about half grown. It is proposed to compare the transcriptional and translational activities of the Xenopus mitochondrial genetic system during periods of intense replication (early oogenesis) and relative quiescence (late oogenesis) in an attempt to determine the extent of mitochondrial contribution to the "informational" content of the female gamete. A comparison of the abundance of total mitochondrial messenger RNA (mt poly-A ion RNA) isolated from early vs late oocytes will be undertaken using moleclar hybridization with radioactive complementary DNA (cDNA) synthesized from a template of total ovarian mt poly-A ion RNA. Both direct quantitation of mt poly-A ion RNA extracted from different oocyte stages and bound to filters, as well as kinetic analysis of "back hybridization" of poly-A ion RNA to cDNA will be used. If successful with a total poly-A ion RNA fraction, experiments will be extended to individual poly-A ion RNA species isolated by fractionation on denaturing gels. The temporal sequence of mitochondrial protein synthesis during oogenesis will be examined in intact oocytes and in vitro. Mitochondrial polypeptides synthesized by early and late oocytes in the presence of cycloheximide will be compared by SDS-polyacrylamide gel electrophoresis. In vitro translation of isolated mt poly-A ion RNAs in a rat liver submitochondrial system will be used to verify the coding of ATPase and cytochrome oxidase subunits by these RNA species. It is hoped to correlate any differences found in the poly-A ion RNA content during oogenesis with the profile of mitochondrial polypeptides synthesized in vitro.